1. Field of Invention
The present invention relates to a permanently doped polyaniline and its method of production. More specifically, the present invention relates to a permanently doped polyaniline as a film and its production by the electropolymerization of a solution of aniline and an organic dopant, such as an organic sulfonate, and the use of the film in electrical transmission and storage, e.g. as an electrode in an advanced electrical storage battery.
2. Description of Related Art
During the last five years, a great deal of effort has been expended to develop polyaniline-based rechargeable polymer batteries, especially in conjunction with a lithium anode in nonaqueous electrolytes. The doping rate of polyaniline is about twice that of any other conducting polymers, and the stability of polyaniline is probably the best. Recently, the first commercial, coin-shaped polyaniline/lithium battery suitable as a memory back-up power source was developed by T. Kita et al. for Bridgestone/Seiko. See "Properties of Polyaniline Secondary Battery," Abstract No. 24, 170th Electrochemical Society Meeting, San Diego, Calif., October 1986. Table 1 summarizes typical performance characteristics of three secondary battery systems (i.e. lead-acid, nickel-cadmium, and Bridgestone's new polyaniline battery).
The following references relate to Table 1:
A. G. MacDiarmid et al. (1986), Extended Abstracts, Vol. 86, Abstract #2, 170th Electrochemical Society Meeting, San Diego, Calif., Oct. 19-24.
A. Kitani et al., (1986), Journal of the Electrochemical Society, Vol. 133, #6, pp. 1069-1073.
N. Koura et al., Denki Kagaku, Vol. 55, #5, pp. 386-391.
TABLE 1 __________________________________________________________________________ COMPARISON OF DIFFERENT POLYANILINE ELECTRODES MacDiarmid Kitani and Yang et al. Kours and Kijima SRI (1986) (1986) (1987) (Preliminary data) __________________________________________________________________________ Polyaniline electrode powder e.c. polymer powder powder e.c. polymer Starting materials aniline 0.1 M aniline 0.5 M aniline 0.5 M aniline 0.1 M aniline (NH.sub.4).sub.2 S.sub.2 O.sub.4 0.1 M H.sub.2 SO.sub.4 0.1 M HCl 0.1 M H.sub.2 SO.sub.4 1 M tosylate Preparation method chemical PC.sup.d /Pt CP.sup.f /graph CP.sup.f /graph PC.sup.i /Pt Weight of polyaniline (g) -0.04 (2 .times. 2 cm) 57 5 -0.024 Electrolyte PC/LiClO.sub.4 1 M ZnSO.sub.4 AlCl.sub.3 /BPC.sup.g 0.5 M ZnSO.sub.4 1 M ZnSO.sub.4 (pH 4.6) (pH 2.3) Anode (negative elec- Li Zn (beads) Al Zn sheet Zn sheet trode) Open-cell voltage (V) 3.3 -1.1 1.7 1.4 1.3 Short-circuit current (mA) -- -- -- -- 3.0 Capacity (Ah/kg) 147.7.sup.b -106 130 100 -36 Capacity.sup.a (Ah/kg) 92.7 -- -- -- -- Power density (kW/kg) -- -- -- -- 0.2 Energy density (Wh/kg) 539.2.sup.c &lt;111 180 -140 -39 Energy density.sup.a (Wh/kg) 338.3 -- -- -- -- Coulomb efficiency (%) -- 100.sup.e 85-90.sup.h -85.sup.i -86.sup.k Cycle life (cycles) -- &lt;2000.sup.e -60.sup.h -60.sup.i &gt;400.sup.l Self-discharge rate 57 -- 6 -- high (%/month) __________________________________________________________________________ .sup.a Including the weight of electrolyte. .sup.b Discharge rate of 0.2 mA/cm.sup.2. .sup.c At an average discharge voltage of 3.65 V. .sup.d Potential cycle (100 mV/s) for 1000 times between -0.2 V and +0.8 vs. SCE. .sup.e Cycled between 1.35 V and 0.75 V at a constant current density of mA/cm.sup.2. .sup.f Constant potential of 1 V vs. SCE for 72 hours using graphite electrode. .sup.g 2:1 mixture of AlCl.sub.3 and 1butylpyridinium chloride. .sup.h At .+-.4 mA/cm.sup.2. .sup.i At .+-.2 mA/cm.sup.2. .sup.j Potential cycle (100 mV/s for 4 hours between -0.2 V and +0.8 V vs. SCE at 30.degree. C. .sup.k Cycled between 1.35 V and 0.75 V at .+-.10 mA/cm.sup.2. .sup.l At .+-.10 mA/cm.sup.2.
The T. Kita/Bridgestone polyaniline battery offers attractive characteristics such as high operating voltage, good cycle life and low self-discharge rate. In addition, polyaniline batteries in general appear to be intrinsically superior to other existing secondary batteries because of potentially high charge capacity and high energy density (features not yet realized in the Bridgestone battery). Furthermore, although the polyaniline/lithium nonaqueous battery developed by Bridgestone/Seiko is said to exhibit excellent shelf-life, i.e., little self-discharge, there are difficulties associated with the use of a nonaqueous solvent (e.g. propylene carbonate) in conjunction with a lithium electrode in rechargeable batteries, including:
1. Low capacity (less than 0.004 Ah) and low current output (less than 5 mA).
2. Corrosion is a problem: the lithium surface is gradually covered by some passive film such as Li.sub.2 CO.sub.3 during the repeated cycling of charge and discharge.
3. The high cathodic potential of the Li/Li.sup.+ couple often causes solvent decomposition.
Japanese patent application [JP 62/12073] by Hitachi/Showa Denko discloses the use of tosylate in conjunction with polyaniline. It is apparent that the two batteries are quite different in terms of their fundamental principles. The Hitachi/Showa Denko battery is essentially a conventional polyaniline/Li nonaqueous battery, in which anions such as ClO.sub.4.sup.- are dopants in the positive polyaniline electrode. The tosylate is used merely as a sacrificial material. (Anions with a larger ionic radius, such as tosylate, are added during electropolymerization of aniline. The grown polyaniline film is rinsed thoroughly with water to get rid of the added anions, leaving the polyaniline with a high microporous channel structure through which small anions, e.g. ClO.sub.4.sup.-, can easily diffuse in and out).
Organic conducting polymers such as polypyrrole (PPy), polythiophene (PTP), polyaniline (PAn or PAN) and their derivatives are gaining in popularity for potential use in optical, electronic and electrochemical devices. See, for example, F. Garnier et al., Journal of Electroanalytical Chemistry (1983), Vol. 148, p. 299; H. Kaezuka, et al., Journal of Applied Physics (1983), Vol. 54, p. 2511; and A. Mohammadi et al., Journal of the Electrochemical Society (1986), Vol. 133, p. 947.
A major disadvantage of these electrically conducting polymers in any configuration is that they usually have poor mechanical properties. See, for example, O. Niwa, et al., Journal of the Chemical Society (1984), p. 817; S. E. Lindsey, et al., "Synthetic Methods," (1984/1985), Vol. 10, p. 67; F. R. F. Fan, et al., Journal of the Electrochemical Society, Vol 133, p. 301; and R. M. Penner, et al., Journal of the Electrochemical Society (1986), Vol. 133, p. 310.
Several approaches may be useful to improve the physical and mechanical properties of the conducting polymers. For instance, the polymerization of pyrrole in thick electroactive polymer networks such as poly(vinychloride), poly(vinyl alcohol), NAFION.RTM., a trademark of the E. I. DuPont Co., Inc. of Wilmington, Del., for a perfluorinated sulfonic acid material and membrane, and NAFION.RTM.-impregnated GORE-TEX.RTM., where GORE-TEX.RTM. is a trademark of W. F. Gore and Associates of Elkton, Md., for a porous polytetrafluoroethylene material has been reported in the literature.
T. Harai, et al., Journal of the Electrochemical Society (1988), Vol. 135 (#5), p. 1132-1137 reported that the anodic polymerization of pyrrole, 3-methylthiophene and aniline at NAFION-coated electrodes gives electrically conducting polyaniline (NAFION) composite films. These composites show an improvement of the polypyrrole electrochromic response and by the efficient utilization of stored charge by the composite film electrodes.
All of the disclosure in the references cited herein are incorporated herein by reference.
These references do not teach or suggest a permanently doped polyaniline for use as a secondary battery as is described in the present invention.